This invention relates generally to the field of hard disc drive data storage devices, and more particularly, but not by way of limitation, to an improved mounting system for attaching the head suspensions that support the read/write heads to the head mounting arms of the disc drive actuator.
Disc drives of the type known as xe2x80x9cWinchesterxe2x80x9d disc drives or hard disc drives are well known in the industry. Such disc drives record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 10,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator housing opposite to the coil, the actuator housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator housing rotates, the heads are moved radially across the data tracks along an accurate path.
The head suspensions mentioned above are typically formed from thin stainless steel foil. In order to provide a robust connection between the head suspension and the actuator head mounting arms, the attachment end of the head suspension is typically welded to a relatively thick mounting plate which includes features intended to cooperate with mating features on the actuator head mounting arms to attach the head suspensions to the actuator.
By far the most common head suspension mounting method in current use is swage mounting. Swage mounted head suspensions include mounting plates that are formed with a cylindrical swage boss. Typically, the entire array of head/suspension assemblies is placed in cooperative arrangement with the actuator head mounting arms, with the swage bosses of the head suspension mounting plates inserted into openings in the actuator head mounting arms. A swaging tool, consisting of a ball feature having a diameter slightly larger than the inner diameter of the swage bosses, is then passed through the entire vertically aligned stack of swage bosses, plastically deforming the swage bosses and expanding the swage bosses into firm contact with the inner diameters of the openings in the actuator head mounting arms. Thus, swage mounting of the head/suspension assemblies is simple and economical for use in high volume manufacturing environments.
Swage mounting of head suspensions does, however, produce potential problems. Firstly, the plastic deformation of the swage bosses during the swaging process induces large mechanical stresses in the material of the mounting plates, and these mechanical stresses can lead to deformation of the planar portion of the mounting plates to which the thin head suspensions are welded. Such deformation can lead to changes in the gram load applied by the head suspension to the flying head assembly. As is well known to those of skill in the art, one of the principal functions of the head suspension is to provide a load force, typically referred to in the industry as gram load, to counteract the hydrodynamic lifting force of the slider assembly of the head. In order to accurately maintain the 2.0 to 1.5 microinch (0.000002 to 0.0000015 inch) flying heights of the heads specified in disc drives of the current generation, it is essential to balance the gram load with the lifting force of the head to a very precise degree. The gram load of the head/head suspension assembly is typically set after the mounting plates are welded to the head suspension, but before the complete mounting plate/head suspension/head assembly is mounted within the disc drive.
It has been noted in the industry that swage mounting of the head suspensions alters the preset gram load of the suspension. That is, if a desired pre-swaging gram load is established at the sub-assembly level, the act of swaging results in a detrimental difference in the post-swaging gram load, and, most significantly, to differing changes to xe2x80x9cupxe2x80x9d and xe2x80x9cdownxe2x80x9d head/head suspension assemblies. This difference in alteration of the gram load for xe2x80x9cupxe2x80x9d and xe2x80x9cdownxe2x80x9d assemblies is referred to in the industry as xe2x80x9cup/down biasxe2x80x9d, and affects not only the flying height of the head assemblies, but, of greater significance, the resonant frequencies of the head/head suspension assemblies.
Finally, swage mounting, by definition, plastically deforms the associated components when it is performed. If, after assembly, a faulty component is discovered, it is difficult to disassembly a swage mounted head suspension assembly without damaging other xe2x80x9cgoodxe2x80x9d components. Additionally, reinsertion of a replacement swage mounted head suspension into a head mounting arm that has already been stressed by a previous swaging operation may result in less than optimal mounting force, leading to undesirable variation in the finished product.
An additional potential drawback to typical prior art suspension mounting systems lies in the previously mentioned welding of the head suspensions to the robust mounting plates. This welding is typically accomplished by use of a high intensity laser, and can result in localized stress in the thin foil of the head suspension, again potentially leading to undesirable variation in the static pitch and roll characteristics of the entire head suspension.
For these and other reasons to be noted below, a need clearly exists for an alternative to swage mounting of the head suspension assemblies in a disc drive.
The present invention is an improved system for mounting the head suspensions to the actuator mounting arms of a disc drive actuator. The mounting system of the invention includes novel features on both the head suspension mounting plates and on the actuator head mounting arms that facilitate head suspension mounting without the introduction of plastic deformation in any of the mounting elements. The mounting plate of the invention includes a boss and a hole. The boss and hole are dimensioned for interference fit with complementary elements on a second mounting plate located on the opposite side of the actuator head mounting arm, to provide the retention force of the mounting system. The bosses of the mounting plates also form an interference fit with cooperative holes in the actuator head mounting arm. Compliance features are included with the holes on the actuator head mounting arm to prevent plastic deformation of the material of the head mounting arm.
It is an object of the invention to provide a mounting system for attaching head suspensions to actuator head mounting arms in a disc drive.
It is another object of the invention to provide a mounting system for attaching head suspensions to actuator head mounting arms in a disc drive that is self-aligning.
It is another object of the invention to provide a mounting system for attaching head suspensions to actuator head mounting arms in a disc drive that does not cause plastic deformation of the system elements, and which thus allows for simple removal and replacement of detected faulty components without altering the retention characteristics of the head suspension mounting system.
It is another object of the invention to provide a mounting system for attaching head suspensions to actuator head mounting arms in a disc drive that does not cause plastic deformation of the system elements, and which thus eliminates up/down bias in the gram load of the head suspension brought about by the mounting process.
It is another object of the invention to provide a head suspension mounting system for a disc drive that is simple and economical to implement in a high volume manufacturing environment.
The manner in which the present invention achieves these objects, as well as other features, benefits and advantages of the invention, can be best understood by a review of the following Detailed Description of the Invention, when read in conjunction with an examination of the accompanying drawings.